1. Field of the Invention
The present invention relates to a portable file system in which files stored in a portable personal data device are accessible from a data processing device for executing a desired processing on data of the files.
2. Description of the Background Art
In a currently popular distributed computing environment, a plurality of work stations or personal computers are connected by the LAN (Local Area Network), and a file sharing technique such as the NFS (Network File System) developed by SUN Microsystems, Inc. is utilized to offer a network transparent distributed file system environment (i.e., an environment in which a file can be utilized without being conscious of a computer in which this file is actually stored) to the user.
The NFS also conceals a difference between different types of file systems coexisting in the distributed computing environment by a mechanism called Virtual File System Interface, so as to support a device type transparency. In this Virtual File System Interface, requests and data are exchanged between a file server side which discloses a content of its file system to another host and a client side which makes an access to a content of a file system possessed by another host, by defining a common file system interface. Each file server or client has an interface in correspondence to a file system possessed by its own host, so that in order to make a file access through a network, there is a need for a conversion with respect to a common interface at the server side as well as at the client side.
For this reason, the file system realizing the NFS has a configuration as shown in FIG. 1. In this configuration of FIG. 1, a file access request from a computer-1 1010 is given to a Virtual File System Interface 1011 on the computer-1 side first, and then, for a file in its own database 1013, the access is made through a Unix File System 1012 on the computer-1 side. On the other hand, for a file in a database 1024 of a computer-2 1020, the request is transmitted from a NFS Client 1014 on the computer-1 side through a network 1000 to a NFS Server 1021 on the computer-2 side. Then, the NFS Server 1021 issues the request to a Virtual File System Interface 1022 on the computer-2 side, from which the access is made through a Unix File System 1023 on the computer-2 side.
Now, a scale in which the above described network transparent distributed file system environment can be provided is limited by a total number of computers involved as well as by geographic or organizational constraints. For instance, the network transparent distributed file system environment is usually provided in units of a section or a research center in the case of a company, or in units of a research group or a department in the case of a university.
On the other hand, in conjunction with the wide spread use of computers, use of a computer is becoming an integral part of our work or daily life, and a situation calling for a use of a computer is more and more increasing both time-wise and location-wise. For instance, apart from daily work using a computer at a regular working spot in a company, there may be occasions to utilize computers at visiting spots for the purpose of cooperative works with other sections or other organizations, and there may be occasions to utilize a personal computer for work or amusement at home.
Despite such an expansion of situations to utilize a computer, the distributed file system can provide a network transparent file sharing only within a limited environment as described above. For instance, in the NFS including the Virtual File System Interface, it is impossible to share a file among different environments in which the user management data are different (e.g., environments in which different users are assigned to the same user ID).
For this reason, conventionally, a separate file management has been required at each computer environment, e.g., at a working spot, at a visiting spot, and at home. As a consequence, when a certain file is to be shared among these environments, a user can realize such a sharing only by copying this file by utilizing a floppy disk or a communication line. However, in this mode of realizing the file sharing, the user is required to endure the tediousness of carrying out cumbersome copying operations to make copies as well as a careful file management in order to maintain the consistency among the copies, and in addition, the user is held responsible for a considerable risk of data loss resulting from a file management error.